"No two tours of the BBC Television Centre are ever the same," says our guide, Simon Webb. "It all depends which programmes are to be recorded."
And which celebrities are walking the corridors. A frisson of excitement runs through the group of Year 8 boys from York House School, Rickmansworth, but should we see anyone we recognise, we are advised to admire from afar rather than rush up and request an autograph.
First stop is news. "This is the largest news production centre in the world," boasts our second guide, Elizabeth Keates. It is trimedia - television, radio and internet - and employs more than 2,000 people. We look through huge windows into the newsroom which is a sea of monitors, with larger screens beaming in images from around the world. "We are gathering news via our reporters in every major city and from agencies such as Reuters. Members of the public are also encouraged to send in items but we check and double check before we use anything to make sure it is a true story."
The Stagedoor is the area where all the artistes arrive. "You may recognise this as the place the Jet Set Lottery winners rush out to their waiting limo," says Simon. "All the contestants are filmed getting in the limo so that the shot of the winning couple is ready for the final moments."
The layout of the BBC TV Centre, opened in 1960, seems unnervingly Kafkaesque. Architect Graham Dawbarn designed the building to fit into the pizza-shaped piece of land available. Doodling on an envelope, he came up with a question mark shape, with the studios, recording areas, offices and others in the rounded end and the newsroom as the dot.
The Top of the Pops set draws amazed glances. How could somewhere that looks so cool on television actually be so tatty? There isn't even a proper ceiling, just plastic sheeting. "It's all a matter of lighting," explains Elizabeth. "Why do you think the people on the dancefloor clap with their hands above their heads?" If they clapped normally, you wouldn't be able to see their hands and they would just appear to be swaying slightly.
Peering into studios where Friday Night with Jonathan Ross and The Lenny Henry Show are to be recorded in front of live audiences, the set looks much smaller than on the TV screen. The newest of new technology, laser-controlled lighting, is pointed out, resembling bullseyes up in the dark recesses of the roof. There is an opportunity for the boys to perform in their own mocked-up studio, where they take the roles of contestants, technicians and newsreader in a specially-written quiz show.
The weather department proves a big hit with the boys, especially when they appear on a screen mocked up to demonstrate how the Colour Separation Overlay works when forecasters are speaking to camera. We are shown how the back of the screen is flooded with blue light and an electronic system causes any area where the camera detects blue to be replaced by a "clean feed" of the weather charts from the computer, called up by the forecaster at the touch of a button. The forecasters cannot dress in blue as this would cause them to merge with the graphics.
Checking our security passes back, not a single famous person has been spotted. We make do with a scary photograph of Anne Robinson winking at us as we leave.
* Tours last 90 minutes, booking essential.
School group rate applies to groups of 15 or more and is pound;4.50 for children (seven years and over for CBBC Tours, nine years and over for the general tour), Students (16 and over), pound;5.50 1 free place for every 15 people and any extra teachers pound;6.50. Tours also at regional and local BBC centres.
ON THE MAP
BBC Television Centre
BBC Television Centre, Wood Lane, London W12 7RJ
Tel: 0870 603 0304